Abstract
De novo fatty acid biosynthesis in humans is accomplished by a multidomain protein, the Type I fatty acid synthase (FAS). Although ubiquitously expressed in all tissues, fatty acid synthesis is not essential in normal healthy cells due to sufficient supply with fatty acids by the diet. However, FAS is overexpressed in cancer cells and correlates with tumor malignancy, which makes FAS an attractive selective therapeutic target in tumorigenesis. Herein, we present a crystal structure of the condensing part of murine FAS, highly homologous to human FAS, with octanoyl moieties covalently bound to the transferase (MAT—malonyl‐/acetyltransferase) and the condensation (KS—β‐ketoacyl synthase) domain. The MAT domain binds the octanoyl moiety in a novel (unique) conformation, which reflects the pronounced conformational dynamics of the substrate‐binding site responsible for the MAT substrate promiscuity. In contrast, the KS binding pocket just subtly adapts to the octanoyl moiety upon substrate binding. Besides the rigid domain structure, we found a positive cooperative effect in the substrate binding of the KS domain by a comprehensive enzyme kinetic study. These structural and mechanistic findings contribute significantly to our understanding of the mode of action of FAS and may guide future rational inhibitor designs.
Highlights
Fatty acids are essential molecules in most living cells, serving as key compounds of cell membranes, as energy supply in the metabolism, as secondary messengers in signaling pathways or as covalent modifications to recruit proteins to membranes
The results of this study provide new insights into the key processes of substrate loading and condensation in fatty acid synthesis and foster the development and optimization of inhibitors with potential antineoplastic properties. 117
Following an established protocol (Rittner et al, 2018), the purified murine ketoacyl synthase (KS)-moieties covalently bound to the transferase (MAT) didomain, sharing 87 % sequence identity to the condensing part of human fatty acid synthase (FAS) (Pappenberger et al, 2010), was crystallized and crystals were soaked with octanoyl-CoA (Figure S1)
Summary
Fatty acids are essential molecules in most living cells, serving as key compounds of cell membranes, as energy supply in the metabolism, as secondary messengers in signaling pathways or as covalent modifications to recruit proteins to membranes. They can either be obtained directly from the diet or are synthesized de novo by fatty acid synthases (FASs) from simple building blocks in repeating cyclic reactions. The MAT domain of murine type I FAS shows broad substrate specificity and facilitates the synthesis of methylbranched, odd numbered and functionalized fatty acids by alternative substrate selection (Buckner et al, 1978; Rittner et al, 2019; Rittner et al., 2018; Smith and Stern, 1983). The results of this study provide new insights into the key processes of substrate loading and condensation in fatty acid synthesis and foster the development and optimization of inhibitors with potential antineoplastic properties. 117
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